Recently, a push data distribution service which distributes information to a terminal unit from a server is becoming popular. Such a service is called a PUSH service. In the PUSH service, a terminal unit may receive information automatically whenever the information is delivered from a server, regardless that the terminal unit stays in a power-on state or not or that the terminal unit is connected to a communication network or not.
In order to implement such a service, a terminal unit provided with a remote-controlled communication device has been proposed where the remote-controlled communication device manages the power supply for the terminal unit by waiting for user manipulation. The remote-controlled communication device is provided with its own central processing unit (CPU) and thus may perform, for example, power control of the terminal unit independently from the control caused by the CPU of the terminal unit. Hereinafter, components controlled by the CPU of the terminal unit will be collectively called a “terminal unit main body”, and a state in which the terminal unit main body is in a power-off state will be also expresses as “the terminal unit is in a power-off state” meaning that the terminal unit main body is in a power-off state.
The remote-controlled communication device operates to achieve its own function even when the terminal unit is in a power-off state. Since the remote-controlled communication device operates even when the terminal unit is in a power-off state, the remote-controlled communication device consumes the power at all times. In order to reduce the power consumption, the remote-controlled communication device is usually implemented by a low power consumption circuit using a micro processing unit (MPU) which operates at several or several tens of MHz. Further, the remote-controlled communication device may be connected to a communication network by connecting itself to a communication device via an interface such as a universal serial bus (USB).
With the remote-controlled communication device staying energized at all times, a PUSH service, such as transmitting a push notification and downloading a file, may be provided even when the terminal unit is in a power-off state.
However, since the remote-controlled communication device is implemented at a low clock rate, a transmission device included in the remote-controlled communication device may not be operated at a sufficient transmission rate compared to a transmission device included in the terminal unit main body. When the terminal unit is in a power-off state, that is, the terminal unit main body is in a power-off state, data transmission at a low rate does not affect the operation of the terminal unit since there exist no processes being performed in the terminal unit main body.
On the other hand, when the terminal unit is in a power-on state, that is, the terminal unit main body is in a power-on state, an operator may manipulate the terminal unit so that the terminal unit main body performs some processes. In such a situation, the low transmission rate may cause delay in response, thereby making it difficult to satisfy a requirement of the operator. It is therefore desirable to avoid a situation in which the terminal unit main body acquires data via the remote-controlled communication device when the terminal unit, that is, the terminal unit main body is in a power-on state.
In order to address this problem, a method has been proposed in which, for example, when connection between the terminal unit and a communication device is established via a USB interface, a USB bus capable of connecting the communication device to each of the terminal unit main body and the remote-controlled communication device is selectively switched using a USB bus switch so that one of the terminal unit main body and the remote-controlled communication device is selected as a USB host. This method allows a terminal unit equipped with a remote-controlled communication device to perform always-on connection to a communication network without any reduction in transmission speed.
A related art is proposed in which, in a redundant communication control system, data is saved in a common memory shared by both an active system and a standby system, and the standby system takes over communication control processing from the active system by referring to the common memory at the time of switching the active and standby systems. Another related art is proposed in which any of a plurality of processing circuits provided in a terminal unit is selected to perform protocol processing by switching a bus.
Japanese Laid-open Patent Publication No. 10-145456 and Japanese Laid-open Patent Publication No. 2004-147251 are examples of the related art.